1. Field of the Invention
The present invention relates to a method for surface-alloying metal by utilizing a high-density energy beam, such as a laser beam or an electron beam, and to a surface-alloyed steel. The present invention also relates to a method for working the surface-alloyed metal by the above method.
2. Description of the Related Art
The methods for surface-alloying metal by means of a laser beam or an electron beam presently in the process of development cannot be applied industrially since they involve the problems of the dragging of oxides, the generation of blowholes, nonuniform distribution of an additive, a poor surface roughness, and the like. In addition, laser beams and electron beams are expensive energy sources and, hence, cannot compete well with less expensive energy sources. Nevertheless, since high-density energy such as a laser beam or an electron beam can be easily controlled and can provide a working means for a completely automatic working plant, the provision of a method for surface-alloying metal by means of high-density energy and the subsequent metal-working method is desired in the present field. The working herein means any treatment for providing metal with a surface property and a shape which make the metal appropriate for use as machine parts and tools and for other industrial applications.
It is known to irradiate the surface of metallic material with a high-density energy beam while an additive is sprayed onto the surface. In this alloying method, the concentration of the alloying element(s) is nonuniformly distributed in the molten metal. Especially when a laser beam is used, the high-speed gas stream used for blowing out the plasma cloud scatters the additive, resulting in a reduction of the concentration of the additive in the melt.
It is also known to melt the additive in the form of a wire or a ribbon by means of a high-density energy beam and to drop the molten additive onto a surface of the metallic material while irradiating it with a high-density energy beam. This alloying method also does not provide a uniform concentration of the alloying element(s) in the molten metal.
The known methods do not provide certain qualities and a lower production cost of the surface-alloyed metal, and therefore they are not industrially applied.
The present applicant tried to improve the known methods mentioned above by melting a surface of a base metal which had undergone the application or fusion-bonding of an additive. The improvement was appreciable. However, the tried method could not be practiced.